The invention relates, to a television camera tube comprising, in an evacuated envelope, an electron gun for generating at least one electron beam. The electron beam is focused onto a target having a photosensitive layer. The beam is deflected over the target. A grid electrode having hexagonal apertures is provided directly in front of the target.
Such a television camera tube is described in Japanese Kokai No. 58-7752. In the tube described therein, a grid electrode is provided a few millimeters away from the photosensitive layer. The electric field between the grid electrode and the photosensitive layer ensures that the electron beam lands on the target substantially perpendicularly over the entire photosensitive layer.
Moire effects, which arise when the grid electrode is scanned by an electron beam along a line pattern, are less liable to occur if the apertures in the grid electrode are hexagonal. However, the process of imparting a hexagonal shape to the apertures, as described in Japanese Kokai No. 58-7752 which is considered to be incorporated herein by reference, results in a reduction of the electron transmission as compared with the transmission of the commonly used grid electrode having square apertures.
The grid electrode is tensioned in order to reduce microphonics in the tube. The maximum tension is then limited by the tensile strength of the grid electrode.